Abstract
The rheological behavior of a waxy crude oil was investigated using a coaxial cylinder viscometer. Experimental flow curves were fitted with the Casson equation. The Casson model was modified to interpret the hysteresis between upward and downward curves obtained in a series of consecutive runs. At the same shear rate, the mean axial ratio of the flow unit related to a down-curve (↓) is smaller than that related to an equilibrium up-curve (↑). This results in a decrease of the Casson yield stress τc↓ with respect to τc↑. A certain ξ coefficient describing departure from the equilibrium mean axial ratio was introduced into the model. Values of ξ calculated from the Casson yield stresses agreed satisfactorily with the theoretically predicted ones. Deviations from the Casson model at low shear rates were also explained.
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Received: 28 July 1998 Accepted: 18 February 1999
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Kirsanov, E., Remizov, S. Application of the Casson model to thixotropic waxy crude oil. Rheol. Acta 38, 172–176 (1999). https://doi.org/10.1007/s003970050166
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DOI: https://doi.org/10.1007/s003970050166